Recently, preliminary research using cyclotron produced, positron emitting radiolabels has been conducted at the Memorial Sloan Kettering Cancer Center to develop a rabbit/rat corneal implant method to study human tumor angiogenesis and metabolism. This technique is designed to determine the impact of chemotherapeutic strategies directly on human brain tumors and provides the hope that drug screening for patients with gliomas can be carried out with sufficient efficacy that a substantial increase in the long term survival rate of such patients can be achieved. To develop such a protocol, unique equipment is needed to measure the accumulation of positron labeled amino acids within the tumor with high sensitivity and spacial resolution despite the presence of an extremely large background from the associated 511 key gamma rays. We propose a program to develop a small, solid state, dual element positron-gamma probe specifically designed for use with the positron emitting isotopes central to the development of this bioassay. Such a low cost, non-imaging system which will allow high quality measurements of metabolic indices for basic and applied medical research will be a useful addition to the capabilities of medical cyclotron groups.